1. Field of the Invention
The present invention relates to a method of and an apparatus for manufacturing semiconductor devices and, more in particular, it relates to a method of manufacturing semiconductor devices of transporting wafers by way of a load lock chamber of conducting heating for the wafers simultaneously with evacuation into a reaction chamber for conducting processing under heating at a reduced pressure.
2. Description of Related Art
Along with progress for improvement of the performance and increase for the degree of integration of semiconductor devices in recent years, the performance of LP (low pressure)-CVD apparatus has also been improved. In a vertical type LP-CVD apparatus, wafers are once stayed in a load lock chamber (preliminary vacuum chamber) and then transported into a reaction chamber for maintaining vacuum in the vacuum reaction chamber and preventing growth of spontaneously oxidized films to silicon wafers.
As shown in FIG. 4, a load lock type vertical LP-CVD apparatus 1 comprises a vertical reaction furnace (reaction chamber 3) having an outer tube 2a closed at a dome-shaped upper end and closed at a lower end, and an inner tube 2b also made of quartz disposed in the outer tube 2 and opened at both upper and lower ends. The outer tube 2a and the inner tube 2b are secured at the circumferential edge of each of their lower ends to a cylindrical flange 4, and a load lock chamber 5 in communication with the reaction furnace 3 by way of the inner tube 2b is attached to the lower end of the flange 4. A jig 6, referred to as a quartz boat which is made, for example, of quartz glass at high purity and adapted to move vertically along a lifting shaft 5a protruded at the bottom (refer to FIGS. 5A and 5B) and enter the inner tube 2b upon upward movement is contained in the load lock chamber 5.
A plurality of vertically arranged shelves are disposed to the quartz boat 6, and about 100 to 150 silicon wafers can be contained at once by the shelves. The quartz boat 6 is secured on a boat base 7 having a boat cap 7a at the lower end. The boat cap 7a comprises a plate of a diameter larger than that of a lower end opening of the flange 4, so that the quartz boat 6 entering the inner tube 2b stops its upward movement upon abutment of the boat cap 7a against the lower end of the flange 4 and tightly seals the inside of the reaction chamber.
A reaction furnace heater 8 surrounding the outer tube 2a is disposed to the outside of the outer tube 2a such that the temperature of the quartz boat 6 entering the inner tube 2 can be elevated. The flange 4 has an exhaust port 4a in communication with a gap defined between the inner tube 2a and the outer tube 2b, and the load lock chamber 5 has an evacuating exhaust port 5b formed in communication with a vacuum pump (not illustrated) for instance. An exhaust pipe 4b is attached to the exhaust port 4a and an exhaust pipe 5c is attached to the evacuating exhaust port 5b, respectively.
A method of film formation of silicon wafers by the load lock type vertical LP-CVD apparatus 1 will be explained below.
At first, as shown in FIG. 4, after containing silicon wafers in the quartz boat 6 in the load lock chamber 5, the load lock chamber 5 is evacuated through the evacuating exhaust port 5b. In this case, the lower end opening of the flange 4 is closed on the side of the load lock chamber 5 by a furnace opening cap 9, and the reaction furnace 3 and the load lock chamber 5 are isolated. The inside of the reaction furnace 3 is evacuated and the temperature in the furnace is kept at a film-forming temperature by CVD system, for example, at about 750 to 850.degree. C.
Then, as shown in FIG. 5A, the furnace port cap (not illustrated) is opened and the quartz boat 6 is raised to transport the quartz boat 6 from the load lock chamber 5 to the reaction chamber 3. The temperature of the quartz boat 6 transported to the reaction furnace 3 is elevated from the temperature in the load lock chamber which is at a normal temperature to a higher temperature in the reaction furnace (750 to 850.degree. C.).
Subsequently, as shown in FIG. 5B, when the boat cap 7a abuts against the lower end of the flange 4 to tightly close the lower end opening, the quartz boat 6 entering into the reaction furnace 3 stops its upward movement and furnace entry is completed. After completing the furnace entry, the inside of the reaction furnace 3 is purged with nitrogen (N.sub.2) and then film-forming processing for the silicon wafers is conducted in the reaction furnace 3 under heating at a reduced pressure.
However, the quartz boat 6 entering the reaction furnace 3 is put to a large temperature difference from the room temperature in the load lock chamber 5 to a high temperature region at 750 to 850.degree. C. If the boat is transported under such a large temperature difference in a short period of time, since silicon wafers are deformed by abrupt temperature change, particles are formed or cracks referred to as slips are caused due to friction at a portion of the silicon wafers in contact with the quartz boat 6 (portion supporting the silicon wafers). Therefore, it has been necessary to enter the quartz boat 6 containing the silicon wafers at an extremely low entering speed of about 50 mm/min.
As a result, in a case of a quartz boat 6 containing 150 sheets of 8 inches silicon wafers, since the boat length is about 1.5-2 m, it takes about 20 to 30 min of furnace entery time, which gives an undesired effect on the throughput to result in a large factor of hindering the improvement of the reactivity.